Ultrasensitive fiber sensor with enhanced Vernier effect for simultaneous measurements of transverse load and temperature.

Based on enhanced Vernier effect, a compact fiber sensor with ultrahigh sensitivity is proposed for simultaneous transverse load (TL) and temperature measurements. A single mode fiber (SMF) is spliced with a segment of hollow-core fiber (HCF) coated with polydimethylsiloxane (PDMS), some PDMS is injected into the HCF, forming a Vernier sensor with an air cavity adjacent to a PDMS cavity. It is shown that TL and temperature changes give rise to opposite and remarkable different variations in lengths of the two cavities, thereby enhancing Vernier effect and in favor of simultaneous measurements of TL and temperature. Moreover, the limited sensitivity magnification due to the length mismatch between the two cavities is compensated for by reconstructing the Vernier envelope with a broadened free spectrum range (FSR) from output signal. As a result, the highest TL sensitivity reported so far of -2637.47 nm/N and a good condition number of 69.056 for the sensitivity coefficient matrix have been achieved.

Compact Vernier sensor with an all-fiber reflective scheme for simultaneous measurements of temperature and strain.

We propose an all-fiber reflective sensing scheme to simultaneously measure temperature and strain. A length of polarization-maintaining fiber serves as the sensing element, and a piece of hollow-core fiber assists with introducing Vernier effect. Both theoretical deductions and simulative studies have demonstrated the feasibility of the proposed Vernier sensor. Experimental results have shown that the sensor can deliver sensitivities of -88.73 nm/°C and 1.61 nm/µÎµ for temperature and strain, respectively. Further, Both theoretical analyses and experimental results have suggested the capability of simultaneous measurement for such a sensor. Significantly, the proposed Vernier sensor not only presents high sensitivities, but also exhibits a simple structure, compact size and light weight, as well as demonstrates ease of fabrication and hence high repeatability, thus holding great promise for widespread applications in daily life and industry world.

Effect of the optical power factors on the laser-linewidth measurements.

In this paper, the effects of optical power factors like laser power, the powers of the laser beams in the two arms of the optical system, and the power of the photodetector on laser-linewidth measurements are studied. From the experiments, it can be found that when the average optical input power for the photodetector is about 50% of its linear saturation power, the measured laser line width is a minimum. When the optical powers of the laser beams in the two arms are equal in short-delay self-homodyne system, the measured laser line width is narrowest. In the low output power range of the laser, its line width decreases with the increase in optical power. By comparing experiments, it can also be clear that the conventional measurement method is seriously affected by different noise types, which causes the measured line width to become wider and not change even if the laser linewidth changes. However, based on the short-delay coherent envelope method, the measured coherent envelope changes significantly when the laser line width changes slightly, and its corresponding laser-linewidth values are also clearly visible. It confirms the low noise and high resolution of the short-delay self-homodyne coherent-envelope laser-measurement method. The outcomes of this study can provide helpful information for precision ultra-narrow laser-linewidth measurements.

Precise laser linewidth measurement by feature extraction with short-delay self-homodyne.

We propose a precision measurement method of laser linewidth based on short-delay self-homodyne, using the second peak-valley difference (SPVD) feature of the coherent power spectrum to fit laser linewidth. The SPVD model of the self-homodyne coherent envelope spectrum was established. One-to-one correspondence among the values of SPVD, the delay length, and the laser linewidth was determined theoretically and through simulations, while the reliability and stability of the method was verified experimentally. By comparing the detected results, it is found that the fitted laser linewidth obtained by the self-homodyne system is closer to its true value than that obtained by the self-heterodyne system. Hence, the simpler structure of the short-delay self-homodyne coherent envelope laser linewidth measurement method proposed is expected to substitute the previous laser linewidth measurement method, including complex short-delay self-heterodyne coherent envelope laser linewidth measurement method and traditional self-homodyne/heterodyne laser linewidth measurement method, to achieve more precise laser linewidth value.

Signal processing assisted Vernier effect in a single interferometer for sensitivity magnification.

The Vernier effect magnifies optical sensitivity by the superposition of two spectra with slightly shifted frequencies from a sensing interferometer (SIM) and a reference interferometer (RIM). In this study, we demonstrate that the Vernier effect can be obtained through a single interferometer, which detects the changed signal and provides an artificial reference spectrum (ARS) to be superposed with the changed signal spectrum. The ARS extracted by spatial frequency down-conversion of one sensing spectrum in the signal processing is not affected by environmental changes and can be detuned at an arbitrarily small amount with the measured signal spectrum. This approach is simpler and accurate and provides ultrahigh sensitivity. To validate the principle, a Mach-Zehnder (MZ) interferometer based on a dual-mode microfiber was designed for sensing the refractive index (RI) change magnification, and a high sensitivity of 71354.58 nm/refractive index unit (RIU) was obtained with good linearity.

Exponential Synchronization of Markovian Jump Neural Networks Based on Asynchronous Delayed-Feedback Controller With Uncertain Hidden Information.

Due to the complex network environment, the feedback information cannot be timely received by the controller. This article proposes a method on the exponential synchronization for the Markovian jump neural networks, which is achieved by designing a new asynchronous delayed-feedback controller, with its feedback delay taken into account. The quantized relationship between the exponential synchronization and the feedback delay is derived from a new designed Lyapunov functional, to acquire delay boundaries. With the help of a hidden-Markov process, the designed controller shows asynchrony, which allows controller modes to run free. In particular, the detection probability is assumed to be bounded known, marking a breakthrough over existing results. Moreover, the proposed method proves to be applicable in both synchronous and asynchronous cases. By using the proposed method, the computation freedom of the controller gain matrix can be substantially augmented. Further, comparative numerical studies are implemented to validate the effectiveness and superiority of the proposed method.

Endlessly single-polarization single-mode holey fibers with low confinement loss.

We present a novel structure for holey fibers (HFs) with endlessly single-polarization single-mode characteristics, which is realized by introducing four elliptical airholes arranged in a hexagonal matrix in the core region. The validation of the design is done by use of a full-vectorial finite element method. We exhibit one typical design that can deliver a single-polarization single-mode region of more than 2400 nm with a confinement loss level lower than 0.01 dB/km. We have also shown that the persevered polarization state possesses a wide wavelength band of flat dispersion behavior. As a consequence, such HFs are useful in high-speed communication systems or optical-fiber sensors since they are free of polarization mode dispersion and simultaneously immune to cross-talk effect.

Asynchronous fault detection filtering for Markovian jump systems with output sensor saturation.

In this paper, a robust asynchronous filter is proposed to detect faults in Markovian jump systems with sensor saturations. The proposed filter has a mode different from that of the original system, and is tolerant of external disturbances. The residual is generated to construct an evaluation function that can successfully perform fault detection. Detailed filter matrices can be computed from the existing conditions. Furthermore, practical and comparative simulations are performed to verify the efficiency of the proposed technique.